Henry Gray (18251861). Anatomy of the Human Body. 1918.
The Premolars or Bicuspid teeth (dentes præmolares) are eight in number, four in each arch. They are situated lateral to and behind the canine teeth, and are smaller and shorter than they.
The crown is compressed antero-posteriorly, and surmounted by two pyramidal eminences or cusps, a labial and a lingual, separated by a groove; hence their name bicuspid. Of the two cusps the labial is the larger and more prominent. The neck is oval. The root is generally single, compressed, and presents in front and behind a deep groove, which indicates a tendency in the root to become double. The apex is generally bifid.
The upper premolars are larger, and present a greater tendency to the division of their roots than the lower; this is especially the case in the first upper premolar.
The Molar Teeth (dentes molares) are the largest of the permanent set, and their broad crowns are adapted for grinding and pounding the food. They are twelve in number; six in each arch, three being placed posterior to each of the second premolars.
The crown of each is nearly cubical in form, convex on its buccal and lingual surfaces, flattened on its surfaces of contact; it is surmounted by four or five tubercles, or cusps, separated from each other by a crucial depression; hence the molars are sometimes termed multicuspids. The neck is distinct, large, and rounded.
Upper Molars.As a rule the first is the largest, and the third the smallest of the upper molars. The crown of the first has usually four tubercles; that of the second, three or four; that of the third, three. Each upper molar has three roots, and of these two are buccal and nearly parallel to one another; the third is lingual and diverges from the others as it runs upward. The roots of the third molar (dens serotinus or wisdom-tooth) are more or less fused together.
Lower Molars.The lower molars are larger than the upper. On the crown of the first there are usually five tubercles; on those of the second and third, four or five. Each lower molar has two roots, an anterior, nearly vertical, and a posterior, directed obliquely backward; both roots are grooved longitudinally, indicating a tendency to division. The two roots of the third molar (dens serotinus or wisdom tooth) are more or less united.
The Deciduous Teeth (dentes decidui; temporary or milk teeth) (Fig. 1004).The deciduous are smaller than, but, generally speaking, resemble in form, the teeth which bear the same names in the permanent set. The hinder of the two molars is the largest of all the deciduous teeth, and is succeeded by the second premolar. The first upper molar has only three cuspstwo labial, one lingual; the second upper molar has four cusps. The first lower molar has four cusps; the second lower molar has five. The roots of the deciduous molars are smaller and more divergent than those of the permanent molars, but in other respects bear a strong resemblance to them.
Structure of the Teeth.On making a vertical section of a tooth (Fig. 1005), a cavity will be found in the interior of the crown and the center of each root; it opens by a minute orifice at the extremity of the latter. This is called the pulp cavity, and contains the dental pulp, a loose connective tissue richly supplied with vessels and nerves, which enter the cavity through the small aperture at the point of each root. Some of the cells of the pulp are arranged as a layer on the wall of the pulp cavity; they are named the odontoblasts of Waldeyer, and during the development of the tooth, are columnar in shape, but later on, after the dentin is fully formed, they become flattened and resemble osteoblasts. Each has two fine processes, the outer one